Gametes of both sexes are highly specialized cells with the unique function of transmitting haploid parental genomes and factors required for early embryonic development to the subsequent generation. Identifying gene products specifically expressed in gametes is a key step to understanding the functions of the gamete "transcriptome." We have used several gene identification strategies including degenerate PCR, in silico subtraction, PCR-based subtraction, genome database mining, and GeneChip technology to characterize over 20 novel gonad-expressed genes. During the previous U54 Center grant period, we identified the mouse and human Bmp15 genes and showed that these genes are X-linked and expressed specifically in oocytes. We also showed that a knockout of Bmp15 in mice results in female fertility defects and that BMP15 and GDF9 have synergistic roles in the periovulatory period. In the present proposal, we will focus on three novel gonad-specific genes (Gasz, Tex14, and Tektin3) that our group has identified. We selected these three genes because they are specifically expressed in germ cells, are evolutionarily-conserved in multiple vertebrate species including fish, frogs, mice, rats, and humans, and are hypothesized to play key roles regulating meiosis or sperm motility. To determine the roles of these three genes in development and the processes that control fertility in humans, we will define their biochemical and physiological properties using yeast two-hybrid screens and the generation of knockout mouse models. Together, the abilities to discover novel genes and define their functions in mouse models provide powerful means to study the molecular mechanisms of mammalian gametogenesis and enable us to place these gene products in biological pathways. Importantly, we can translate these findings to the problem of human infertility by identifying causative mutations. The specific aims of these proposed studies are as follows: 1) Characterize the functions of GASZ as a cytoplasmic signaling protein during male and female germ cell meiosis; 2) Study the ability of TEX14 to regulate key phosphorylation events during male meiosis; and 3) Define the functions of TEKTIN3 in sperm motility and male infertility by analysis of mice and humans with deletions and duplications of the chromosomal region encompassing the TEKTIN3 gene. These studies should give us greater insights into the roles of these proteins in germ cell biology. Compromised fertility in knockout models lacking these proteins would demonstrate that these proteins are potential contraceptive targets and possibly mutated in infertile men and women.